Cosmic energy burst disturbs Earth's atmosphere

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"Earth does not exist in splendid isolation"

A press release from Stanford University

Energy burst from an X-ray star disturbed Earth's
environment

Sept. 29, 1998: On the night of August 27th Earth's
upper atmosphere was bathed briefly by an invisible burst of
gamma- and X-ray radiation. This pulse - the most powerful to
strike Earth from beyond the solar system ever detected - had
a significant effect on Earth's upper atmosphere, report Stanford
researchers. It is the first time that a significant change in
Earth's environment has been traced to energy from a distant
star.

"It was as if night was briefly turned into day in the
ionosphere," says Umran Inan, professor of electrical engineering
at Stanford and head of the research group that observed the
atmospheric disturbance. The ionosphere is the portion of the
atmosphere between 60 to 80 kilometers in altitude that plays
an important role in radio communications. So it is quite likely
that the range of high-powered radio stations, which usually
reach much farther at night due to lower ionospheric activity
levels, was suddenly reduced to their lower, daytime ranges during
the burst's five-minute duration, he says.

The characteristics of the unusual gamma-ray burst, the nature
of the unusual X-ray star that appears to be its source, and
the dramatic effect that it had on the ionosphere are the subjects
of a National Aeronautics and Space Agency space science update
being held on Tuesday, Sept. 29, at 2 p.m. ET at NASA Headquarters
in Washington, D.C.

Stanford's Very Low Frequency Research Group operates a string
of stations in North America that use VLF radio transmissions
to monitor changes in the ionosphere, a region that is above
the range of weather balloons and below that of satellites. Normally,
the researchers use the network, called the Holographic Array
for Ionospheric Lightning research (HAIL), to study the effects
that localized phenomena like lightning have on the ionosphere.
But they were perfectly positioned to measure the impact of the
extra-solar energy pulse.

During the five minutes that the gamma- and X-ray radiation
impinged on Earth's upper atmosphere, the researchers found that
the level of ionization or electrical activity in the ionosphere,
which is normally quiescent at night, suddenly flared to daytime
levels, Inan says.

The Stanford scientists saw the effect clearly in stations
monitoring the ionosphere over the western United States, which
were included in the area illuminated by the burst, but not over
the eastern part of the country, which was in shadow. Inan's
group also saw evidence of a 5.16-second pulsation that corresponds
with the X-ray star's previously established rotation rate, indicating
that the ionization in Earth's atmosphere varied in accordance
with the pulsations of the gamma-ray burst.

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In 1988, Inan and Gerald Fishman from the NASA/Marshall Space
Flight Center reported observing a similar, but much smaller,
ionospheric disturbance associated with a gamma-ray burst that
occurred in 1983. At the time, the source of gamma-ray bursts
was unknown. So the most the scientists could claim was that
"this may be the first time that a transient extra-solar
phenomenon has measurably affected a part of the Earth's environment."
Inan's group detected another small disturbance of this type
in 1996, but did not report it.

Kevin Hurley at University of California-Berkeley has used
satellite information to calculate the total energy that an X-ray
star, called SGR 1900+14, must have released to produce the August
27 burst. He calculates that, if the energy could be harnessed,
it would be enough to power all of human civilization on Earth
for a billion billion years. Of course, only a tiny fraction
of this energy reached Earth.

According to space agency scientists, the radiation reaching
Earth had an intensity slightly less than that of a dental X-ray.
Both gamma rays and X-rays cause ionization directly, by stripping
electrons from atoms and leaving them electrically charged. Nevertheless,
the burst had a remarkable impact on the ionosphere.

"It is amazing that such a burst could produce ionization
levels similar to those produced by all the radiation coming
from the sun," Inan says. "When we put this information
into our mathematical models it may provide us with important
new insights about how the ionosphere behaves in response to
sudden ionization changes."

The nature and intensity of the Aug. 27 gamma ray burst supports
the theory that SGR 1900+14 is an exotic object called a magnetar
predicted by Robert Duncan of the University of Texas-Austin
and Christopher Thompson of the University of North Carolina-Chapel
Hill.

A magnetar is a special kind of neutron star. A neutron star
is the collapsed core that is left behind when a massive star
explodes. It is extremely dense, weighing more than the sun but
squeezed into a ball less than 12 miles in diameter. A magnetar
differs from an ordinary neutron star by possessing a magnetic
field far greater than any other object known. Its field would
be so intense that a steady X-ray glow would emanate from its
surface and periodic starquakes would produce bursts of gamma
rays and occasional cataclysmic flares like the one observed
on August 27.

"All this goes to show that the Earth does not exist
in splendid isolation," says Inan. "We now know that
the Earth's physical environment is affected not only by our
own sun but by energy originating from distant parts of our universe."